Soft tissue paper having a chemical softening agent applied onto a surface thereof

ABSTRACT

A tissue paper product having at least one ply wherein only one outer surface of the tissue paper product has a chemical softening agent applied and substantially affixed thereto is disclosed. The chemical softening agent provides the tissue paper product with a raw dispensing dust value. The raw dispensing dust value is at least about 13.6 percent less than the raw dispensing dust value of a tissue paper product not having the chemical softening agent applied and substantially affixed thereto.

FIELD OF THE INVENTION

This invention relates, in general, to tissue paper products. Morespecifically, it relates to tissue paper products containing chemicalsoftening agent.

BACKGROUND OF THE INVENTION

Sanitary paper tissue products are widely used. Such items arecommercially offered in formats tailored for a variety of uses such asfacial tissues, toilet tissues and absorbent towels.

All of these sanitary products share a common need, specifically to besoft to the touch. Softness is a complex tactile impression elicited bya product when it is stroked against the skin. The purpose of being softis so that these products can be used to cleanse the skin without beingirritating. Effectively cleansing the skin is a persistent personalhygiene problem for many people. Objectionable discharges of urine,menses, and fecal matter from the perineal area or otorhinolaryngogicalmucus discharges do not always occur at a time convenient for one toperform a thorough cleansing, as with soap and copious amounts of waterfor example. As a substitute for thorough cleansing, a wide variety oftissue and toweling products are offered to aid in the task of removingfrom the skin and retaining the before mentioned discharges for disposalin a sanitary fashion. Not surprisingly, the use of these products doesnot approach the level of cleanliness that can be achieved by the morethorough cleansing methods, and producers of tissue and towelingproducts are constantly striving to make their products compete morefavorably with thorough cleansing methods.

Accordingly, making soft tissue and toweling products which promotecomfortable cleaning without performance impairing sacrifices has longbeen the goal of the engineers and scientists who are devoted toresearch into improving tissue paper. There have been numerous attemptsto reduce the abrasive effect, i.e., improve the softness of tissueproducts.

One area that has been exploited in this regard has been to select andmodify cellulose fiber morphologies and engineer paper structures totake optimum advantages of the various available morphologies.Applicable art in this area include in U.S. Pat. Nos. 5,228,954;5,405,499; 4,874,465; and 4,300,981.

Another area which has received a considerable amount of attention isthe addition of chemical softening agents (also referred to herein as“chemical softeners”) to tissue and toweling products.

As used herein, the term “chemical softening agent” refers to anychemical ingredient which improves the tactile sensation perceived bythe consumer who holds a particular paper product and rubs it across theskin. Although somewhat desirable for towel products, softness is aparticularly important property for facial and toilet tissues. Suchtactile perceivable softness can be characterized by, but is not limitedto, friction, flexibility, and smoothness, as well as subjectivedescriptors, such as lubricious, velvet, silk or flannel, which impartsa lubricious feel to tissue. This includes, for exemplary purposes only,basic waxes such as paraffin and beeswax and oils such as mineral oiland silicone oil as well as petrolatum and more complex lubricants andemollients such as quaternary ammonium compounds with long alkyl chains,functional silicones, fatty acids, fatty alcohols and fatty esters.

Thus, it would be advantageous to provide for the addition of chemicalsofteners to already-dried paper webs either at the so-called dry end ofthe papermaking machine or in a separate converting operation subsequentto the papermaking step. Exemplary art from this field includes U.S.Pat. Nos. 5,215,626; 5,246,545; and 5,525,345. While each of thesereferences represent advances over the previous so-called wet endmethods particularly with regard to eliminating the degrading effects onthe papermaking process, none are able to completely address the overallreduction of dust that accompanies such applications to the dry paperweb.

One of the most important physical properties related to softness isgenerally considered by those skilled in the art to be the strength ofthe web. Strength is the ability of the product, and its constituentwebs, to maintain physical integrity and to resist tearing, bursting,and shredding under use conditions. Achieving a high softening potentialwithout degrading strength has long been an object of workers in thefield of the present invention.

Accordingly, it is an object of the present invention to provide a softtissue paper that emits less dust during use without performanceimpairing sacrifices such as in the strength of the paper.

SUMMARY OF THE INVENTION

The present invention provides for a tissue paper product having atleast one ply wherein only one outer surface of the tissue paper producthas a chemical softening agent applied and substantially affixedthereto. The chemical softening agent provides the tissue paper productwith a raw dispensing dust value. The dust value is at least about 13.6percent less than the raw dispensing dust value of a tissue paperproduct not having the chemical softening agent applied andsubstantially affixed thereto.

The present invention also provides for a through-air dried tissue paperproduct having at least one ply wherein only one outer surface of thetissue paper product has a chemical softening agent applied andsubstantially affixed thereto. The chemical softening agent provides thetissue paper product with a raw dispensing dust value of less than out6485 particles.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term “water soluble” refers to materials that aresoluble in water to at least 3%, by weight, at 25° C.

As used herein, the terms “tissue paper web, paper web, web, paper sheetand paper product” are all used interchangeably to refer to sheets ofpaper made by a process comprising the steps of forming an aqueouspapermaking furnish, depositing this furnish on a foraminous surface,such as a Fourdrinier wire, and removing the water from the furnish asby gravity or vacuum-assisted drainage, forming an embryonic web,transferring the embryonic web from the forming surface to a transfersurface traveling at a lower speed than the forming surface. The web isthen transferred to a fabric upon which it is through air dried to afinal dryness after which it is wound upon a reel.

The terms “multi-layered tissue paper web, multi-layered paper web,multi-layered web, multi-layered paper sheet and multi-layered paperproduct” are all used interchangeably in the art to refer to sheets ofpaper prepared from two or more layers of aqueous paper making furnishwhich are preferably comprised of different fiber types, the fiberstypically being relatively long softwood and relatively short hardwoodfibers as used in tissue paper making. The layers are preferably formedfrom the deposition of separate streams of dilute fiber slurries uponone or more endless foraminous surfaces. If the individual layers areinitially formed on separate foraminous surfaces, the layers can besubsequently combined when wet to form a multi-layered tissue paper web.

As used herein, the term “single-ply tissue product” means that it iscomprised of one ply of uncreped tissue; the ply can be substantiallyhomogeneous in nature or it can be a multi-layered tissue paper web. Asused herein, the term “multi-ply tissue product” means that it iscomprised of more than one ply of uncreped tissue. The plies of amulti-ply tissue product can be substantially homogeneous in nature orthey can be multi-layered tissue paper webs.

As used herein, the term “substantively affixed chemical softeningagent” is defined as a chemical agent which imparts lubricity oremolliency to tissue paper products and also possesses permanence withregard to maintaining the fidelity of its deposits without substantialmigration when exposed to the environmental conditions to which productsof this type are ordinarily exposed during their typical life cycle.Waxes and oils for example are capable of imparting lubricity oremolliency to tissue paper, but they suffer from a tendency to migratebecause they have little affinity for the cellulose pulps which comprisethe tissue papers of the present invention. While not wishing to bebound by theory, the substantively affixed chemical softeners of thepresent invention are believed to interact with the cellulose bycovalent, ionic, or hydrogen bonding any of which are sufficientlypotent to stem migration under normal environmental conditions.

Preferably, the substantively affixed chemical softening agents comprisequaternary ammonium compounds. Preferred quaternary compounds have theformula:

(R₁)_(4-m)—N⁺—[R₂]_(m)X⁻

-   -   wherein:        -   m is 1 to 3;        -   R₁ is a C₁-C₆ alkyl group, hydroxyalkyl group, hydrocarbyl            or substituted hydrocarbyl group, alkoxylated group, benzyl            group, or mixtures thereof;        -   R₂ is a C₁₄-C₂₂ alkyl group, hydroxyalkyl group, hydrocarbyl            or substituted hydrocarbyl group, alkoxylated group, benzyl            group, or mixtures thereof; and        -   X⁻ is any softener-compatible anion are suitable for use in            the present invention.

Preferably, each R₁ is methyl and X⁻ is chloride or methyl sulfate.Preferably, each R₂ is C₁₆-C₁₈ alkyl or alkenyl, most preferably each R₂is straight-chain C₁₈ alkyl or alkenyl. Optionally, the R₂ substituentcan be derived from vegetable oil sources.

Such structures include the well-known dialkyldimethylammonium salts(e.g. ditallowdimethylammonium chloride, ditallowdimethylammonium methylsulfate, di(hydrogenated tallow)dimethyl ammonium chloride, etc.), inwhich R₁ are methyl groups, R₂ are tallow groups of varying levels ofsaturation, and X⁻ is chloride or methyl sulfate.

As discussed in Swern, Ed. in Bailey's Industrial Oil and Fat Products,Third Edition, John Wiley and Sons (New York 1964) tallow is a naturallyoccurring material having a variable composition. Table 6.13 in theabove-identified reference edited by Swern indicates that typically 78%or more of the fatty acids of tallow contain 16 or 18 carbon atoms.Typically, half of the fatty acids present in tallow are unsaturated,primarily in the form of oleic acid. Synthetic as well as natural“tallows” fall within the scope of the present invention. It is alsoknown that depending upon the product characteristic requirements thesaturation level of the ditallow can be tailored from non hydrogenated(soft) to touch, partially or completely hydrogenated (hard). All ofabove-described levels of saturations are expressly meant to be includedwithin the scope of the present invention.

Particularly preferred variants of these softening agents are what areconsidered to be mono or diester variations of these quaternary ammoniumcompounds having the formula:

(R₁)_(4-m)—N⁺-[(CH₂)_(n)—Y—R₃]_(m)X⁻

-   -   wherein:    -   Y is —O—(O)C—, or —C(O)—O—, or —NH—C(O)—, or —C(O)—NH—;    -   m is 1 to 3;    -   n is 0 to 4;    -   each R₁ is a C₁-C₆ alkyl group, hydroxyalkyl group, hydrocarbyl        or substituted hydrocarbyl group, alkoxylated group, benzyl        group, or mixtures thereof;    -   each R₃ is a C₁₃-C₂₁ alkyl group, hydroxyalkyl group,        hydrocarbyl or substituted hydrocarbyl group, alkoxylated group,        benzyl group, or mixtures thereof; and    -   X⁻ is any softener-compatible anion.

Preferably, Y═—O—(O)C—, or —C(O)—O—; m=2; and n=2. Each R₁ substituentis preferably a C₁-C₃, alkyl group, with methyl being most preferred.Preferably, each R₃ is C₁₃-C₁₇ alkyl and/or alkenyl, more preferably R₃is straight chain C₁₅-C₁₇ alkyl and/or alkenyl, C₁₅-C₁₇ alkyl, mostpreferably each R₃ is straight-chain C₁₇ alkyl. Optionally, the R₃substituent can be derived from vegetable oil sources.

As mentioned above, X⁻ can be any softener-compatible anion, forexample, acetate, chloride, bromide, methylsulfate, formate, sulfate,nitrate and the like. Preferably X⁻ is chloride or methyl sulfate.

Specific examples of ester-functional quaternary ammonium compoundshaving the structures detailed above and suitable for use in the presentinvention may include the diester dialkyl dimethyl ammonium salts suchas diester ditallow dimethyl ammonium chloride, monoester ditallowdimethyl ammonium chloride, diester ditallow dimethyl ammonium methylsulfate, diester di(hydrogenated)tallow dimethyl ammonium methylsulfate, diester di(hydrogenated)tallow dimethyl ammonium chloride, andmixtures thereof. Diester ditallow dimethyl ammonium chloride anddiester di(hydrogenated)tallow dimethyl ammonium chloride areparticularly preferred. These particular materials are availablecommercially from Witco Chemical Company Inc. of Dublin, Ohio under thetradename “ADOGEN SDMC”.

Typically, half of the fatty acids present in tallow are unsaturated,primarily in the form of oleic acid. Synthetic as well as natural“tallows” fall within the scope of the present invention. It is alsoknown that depending upon the product characteristic requirements, thesaturation level of the ditallow can be tailored from non hydrogenated(soft) to touch, partially or completely hydrogenated (hard). All ofabove-described levels of saturations are expressly meant to be includedwithin the scope of the present invention.

It will be understood that substituents R₁, R₂ and R₃ may optionally besubstituted with various groups such as alkoxyl, hydroxyl, or can bebranched. As mentioned above, preferably each R₁ is methyl orhydroxyethyl. Preferably, each R₂ is C₁₂-C₁₈ alkyl and/or alkenyl, mostpreferably each R₂ is straight-chain C₁₆-C₁₈ alkyl and/or alkenyl, mostpreferably each R₂ is straight-chain C₁₈ alkyl or alkenyl. Preferably R₃is C13-C17 alkyl and/or alkenyl, most preferably R₃ is straight chainC₁₅-C₁₇ alkyl and/or alkenyl. Preferably, X⁻ is chloride or methylsulfate. Furthermore the ester-functional quaternary ammonium compoundscan optionally contain up to about 10% of the mono(long chain alkyl)derivatives, e.g., (R₂)₂—N+—((CH₂)₂ OH) ((CH₂)₂OC(O)R₃) X⁻ as minoringredients. These minor ingredients can act as emulsifiers and can beuseful in the present invention.

Other types of suitable quaternary ammonium compounds for use in thepresent invention are described in U.S. Pat. Nos. 5,543,067; 5,538,595;5,510,000; 5,415,737, and European Patent Application No. 0 688 901 A2.

Di-quat variations of the ester-functional quaternary ammonium compoundscan also be used, and are meant to fall within the scope of the presentinvention. These compounds have the formula:

In the structure named above each R₁ is a C₁-C₆ alkyl or hydroxyalkylgroup, R₃ is C₁₁-C₂₁ hydrocarbyl group, n is 2 to 4 and X⁻ is a suitableanion, such as a halide (e.g., chloride or bromide) or methyl sulfate.Preferably, each R₃ is C₁₃-C₁₇ alkyl and/or alkenyl, most preferablyeach R₃ is straight-chain C₁₅-C₁₇ alkyl and/or alkenyl, and R₁ is amethyl.

While not wishing to be bound by theory, it is believed that the estermoiety(ies) of the quaternary compounds provides a measure ofbiodegradability. It is believed the ester-functional quaternaryammonium compounds used herein biodegrade more rapidly than doconventional dialkyl dimethyl ammonium chemical softeners.

The use of quaternary ammonium ingredients before is most effectivelyaccomplished if the quaternary ammonium ingredient is accompanied by anappropriate plasticizer. The plasticizer can be added during thequaternizing step in the manufacture of the quaternary ammoniumingredient or it can be added subsequent to the quaternization but priorto the application as a chemical softening agent. The plasticizer ischaracterized by being substantially inert during the chemicalsynthesis, but acts as a viscosity reducer to aid in the synthesis andsubsequent handling, i.e. application of the quaternary ammoniumcompound to the tissue paper product. Preferred pasticizers arecomprised of a combination of a non-volatile polyhydroxy compound and afatty acid. Preferred polyhydroxy compounds include glycerol andpolyethylene glycols having a molecular weight of from about 200 toabout 2000, with polyethylene glycol having a molecular weight of fromabout 200 to about 600 being particularly preferred. Preferred fattyacids comprise C₆-C₂₃ linear or branched and saturated or unsaturatedanalogs with isostearic acid being the most preferred.

While not wishing to be bound by theory, it is believed that a synergismresults from the relationship of the polyhydroxy compound and the fattyacid in the mixture. While the polyhydroxy compound performs theessential function of viscosity reduction, it can be quite mobile afterbeing laid down thus detracting from one of the objects of the presentinvention, i.e. that the deposited softener be substantively affixed.The inventors have now found that the addition of a small amount of thefatty acid is able to stem the mobility of the polyhydroxy compound andfurther reduce the viscosity of the mixture so as to increase theprocessability of compositions of a given quaternary ammonium compoundfraction.

Alternative embodiments of preferred substantively affixed chemicalsoftening agents comprise well-known organo-reactive polydimethylsiloxane ingredients, including the most preferred—amino functionalpolydimethyl siloxane.

A most preferred form of the substantively affixed softening agent is tocombine the organo-reactive silicone with a suitable quaternary ammoniumcompound. In this embodiment the organo-reactive silicone is preferredto be an amino polydimethyl siloxane and is used at an amount rangingfrom 0 up to about 50% of the composition by weight, with a preferredusage being in the range of about 5% to about 15% by weight based on theweight of the polysiloxane relative to the total substantively affixedsoftening agent.

The soft tissue paper of the present invention preferably has a basisweight ranging from between about 5 g/m² and about 120 g/m², morepreferably between about 10 g/m² and about 55 g/m², and even morepreferably between about 10 g/m² and about 30 g/m². The soft tissuepaper of the present invention preferably has a density ranging frombetween about 0.01 g/m³ and about 0.19 g/cm³, more preferably betweenabout 0.03 g/m³ and about 0.6 g/cm³, and even more preferably betweenabout 0.1 g/cm³ and 0.2 g/cm³.

The soft tissue paper of the present invention further comprisespapermaking fibers of both hardwood and softwood types wherein at leastabout 50% of the papermaking fibers are hardwood and at least about 10%are softwood. The hardwood and softwood fibers are most preferablyisolated by relegating each to separate layers wherein the tissuecomprises an inner layer and at least one outer layer.

The tissue paper product of the present invention is preferably creped,i.e., produced on a papermaking machine culminating with a Yankee dryerto which a partially dried papermaking web is adhered and upon which itis dried and from which it is removed by the action of a flexiblecreping blade.

Creping is a means of mechanically compacting paper in the machinedirection. The result is an increase in basis weight (mass per unitarea) as well as dramatic changes in many physical properties,particularly when measured in the machine direction. Creping isgenerally accomplished with a flexible blade, a so-called doctor blade,against a Yankee dryer in an on machine operation.

A Yankee dryer is a large diameter, generally 8-20 foot drum which isdesigned to be pressurized with steam to provide a hot surface forcompleting the drying of papermaking webs at the end of the papermakingprocess. The paper web which is first formed on a foraminous formingcarrier, such as a Fourdrinier wire, where it is freed of the copiouswater needed to disperse the fibrous slurry is generally transferred toa felt or fabric in a so-called press section where de-watering iscontinued either by mechanically compacting the paper or by some otherde-watering method such as through-drying with hot air, before finallybeing transferred in the semi-dry condition to the surface of the Yankeefor the drying to be completed.

While the characteristics of the creped paper webs, particularly whenthe creping process is preceded by methods of pattern densification, arepreferred for practicing the present invention, uncreped tissue paper isalso a satisfactory substitute and the practice of the present inventionusing uncreped tissue paper is specifically incorporated within thescope of the present invention. Uncreped tissue paper, a term as usedherein, refers to tissue paper which is non-compressively dried, mostpreferably by throughdrying. Resultant through air dried webs arepattern densified such that zones of relatively high density aredispersed within a high bulk field, including pattern densified tissuewherein zones of relatively high density are continuous and the highbulk field is discrete.

To produce uncreped tissue paper webs, an embryonic web is transferredfrom the foraminous forming carrier upon which it is laid, to a slowermoving, high fiber support transfer fabric carrier. The web is thentransferred to a drying fabric upon which it is dried to a finaldryness. Such webs can offer some advantages in surface smoothnesscompared to creped paper webs.

Tissue paper webs are generally comprised essentially of papermakingfibers. Small amounts of chemical functional agents such as wet strengthor dry strength binders, retention aids, surfactants, size, chemicalsofteners, crepe facilitating compositions are frequently included butthese are typically only used in minor amounts. The papermaking fibersmost frequently used in tissue papers are virgin chemical wood pulps.Additionally, filler materials may also be incorporated into the tissuepapers of the present invention.

Embodiments of the present invention wherein the substantively affixedsoftening agent comprises a quaternary ammonium compound furthercomprise from about 1% to about 50% of a polyhydroxy compound and fromabout 0.1% to about 10% of a fatty acid, each as a percentage of theweight of the quaternary ammonium compound.

Polyhydroxy compounds useful in this embodiment of the present inventioninclude polyethylene glycol, polypropylene glycol and mixtures thereof.

Fatty acids useful in this embodiment of the present invention comprisesC₆-C₂₃ linear, branched, saturated, or unsaturated analogs. The mostpreferred form of such a fatty acid is isostearic acid.

One particularly preferred chemical softening agent contains from about0.1% to about 70% of a polysiloxane compound.

Polysiloxanes which are applicable to chemical softening compositions ofthe present invention include polymeric, oligomeric, copolymeric, andother multiple monomeric siloxane materials. As used herein, the termpolysiloxane shall include all of such polymeric, oligomeric,copolymeric, and other multiple-monomeric materials. Additionally, thepolysiloxane can be straight chained, branched chain, or have a cyclicstructure.

Preferred polysiloxane materials include those having monomeric siloxaneunits of the following structure:

wherein, R₁ and R₁ for each siloxane monomeric unit can independently beany alkyl, aryl, alkenyl, alkaryl, aralkyl, cycloalkyl, halogenatedhydrocarbon, or other radical. Any of such radicals can be substitutedor unsubstituted. R₁ and R₂ radicals of any particular monomeric unitmay differ from the corresponding functionalities of the next adjoiningmonomeric unit. Additionally, the radicals can be either a straightchain, a branched chain, or have a cyclic structure. The radicals R₁ andR₂ can, additionally and independently be other silicone functionalitiessuch as, but not limited to siloxanes, polysiloxanes, and polysilanes.The radicals R₁ and R₂ can also contain any of a variety of organicfunctionalities including, for example, alcohol, carboxylic acid, andamine functionalities.

Reactive, organo-functional silicones, especially amino-functionalsilicones are preferred for the present invention.

Preferred polysiloxanes include straight chain organopolysiloxanematerials of the following general formula:

wherein each R₁-R₉ radical can independently be any C₁-C₁₀ unsubstitutedalkyl or aryl radical, and R₁₀ of any substituted C₁-C₁₀ alkyl or arylradical. Preferably each R₁-R₉ radical is independently any C₁-C₄unsubstituted alkyl group those skilled in the art will recognize thattechnically there is no difference whether, for example, R₉ or R₁₀ isthe substituted radical. Preferably the mole ratio of b to (a+b) isbetween 0 and about 20%, more preferably between 0 and about 10%, andmost preferably between about 1% and about 5%.

In one particularly preferred embodiment, R₁-R₉ are methyl groups andR₁₀ is a substituted or unsubstituted alkyl, aryl, or alkenyl group.Such material shall be generally described herein aspolydimethylsiloxane which has a particular functionality as may beappropriate in that particular case. Exemplary polydimethylsiloxaneinclude, for example, polydimethylsiloxane having an alkyl hydrocarbonR₁₀ radical and polydimethylsiloxane having one or more amino, carboxyl,hydroxyl, ether, polyether, aldehyde, ketone, amide, ester, thiol,and/or other functionalities including alkyl and alkenyl analogs of suchfunctionalities. For example, an amino functional alkyl group as R₁₀could be an amino functional or an aminoalkyl-functionalpolydimethylsiloxane. The exemplary listing of thesepolydimethylsiloxanes is not meant to thereby exclude others notspecifically listed.

Viscosity of polysiloxanes useful for this invention may vary as widelyas the viscosity of polysiloxanes in general vary, so long as thepolysiloxane can be rendered into a form which can be applied to thetissue paper product herein. This includes, but is not limited to,viscosity as low as about 25 centistokes to about 20,000,000 centistokesor even higher. High viscosity polysiloxanes which themselves areresistant to flowing can be effectively deposited by emulsifying with asurfactant or dissolution into a vehicle, such as hexane, listed forexemplary purposes only.

While not wishing to be bound by theory, it is believed that the tactilebenefit efficacy is related to average molecular weight and thatviscosity is also related to average molecular weight. Accordingly, dueto the difficulty of measuring molecular weight directly, viscosity isused herein as the apparent operative parameter with respect toimparting softness to tissue paper.

References disclosing polysiloxanes include U.S. Pat. Nos. 2,826,551;3,964,500; 4,364,837; 5,059,282; 5,529,665; 5,552,020; and BritishPatent 849,433.

It is anticipated that wood pulp in all its varieties will normallycomprise the tissue papers with utility in this invention. However,other cellulose fibrous pulps, such as cotton linters, bagasse, rayon,etc., can be used and none are disclaimed. Wood pulps useful hereininclude chemical pulps such as, sulfite and sulfate (sometimes calledKraft) pulps as well as mechanical pulps including for example, groundwood, ThermoMechanical Pulp (TMP) and Chemi-ThermoMechanical Pulp(CTMP). Pulps derived from both deciduous and coniferous trees can beused.

Hardwood pulps and softwood pulps, as well as combinations of the two,may be employed as papermaking fibers for the tissue paper of thepresent invention. The term “hardwood pulps” as used herein refers tofibrous pulp derived from the woody substance of deciduous trees(angiosperms), whereas “softwood pulps” are fibrous pulps derived fromthe woody substance of coniferous trees (gymnosperms). Blends ofhardwood Kraft pulps, especially eucalyptus, and northern softwood Kraft(NSK) pulps are particularly suitable for making the tissue webs of thepresent invention. A preferred embodiment of the present inventioncomprises the use of layered tissue webs wherein, most preferably,hardwood pulps such as eucalyptus are used for outer layer(s) andwherein northern softwood Kraft pulps are used for the inner layer(s).Also applicable to the present invention are fibers derived fromrecycled paper, which may contain any or all of the above categories offibers.

In one preferred embodiment of the present invention, which utilizesmultiple papermaking furnishes, the furnish containing the papermakingfibers which will be contacted by the particulate filler ispredominantly of the hardwood type, preferably of content of at leastabout 80% hardwood.

Optional Chemical Additives

Other materials can be added to the aqueous papermaking furnish or theembryonic web to impart other characteristics to the product or improvethe papermaking process so long as they are compatible with thechemistry of the substantively affixed softening agent and do notsignificantly and adversely affect the softness, strength, or lowdusting character of the present invention. The following materials areexpressly included, but their inclusion is not offered to beall-inclusive. Other materials can be included as well so long as theydo not interfere or counteract the advantages of the present invention.

It is common to add a cationic charge biasing species to the papermakingprocess to control the zeta potential of the aqueous papermaking furnishas it is delivered to the papermaking process. These materials are usedbecause most of the solids in nature have negative surface charges,including the surfaces of cellulosic fibers and fines and most inorganicfillers. One traditionally used cationic charge biasing species is alum.More recently in the art, charge biasing is done by use of relativelylow molecular weight cationic synthetic polymers preferably having amolecular weight of no more than about 500,000 and more preferably nomore than about 200,000, or even about 100,000. The charge densities ofsuch low molecular weight cationic synthetic polymers are relativelyhigh. These charge densities range from about 4 to about 8 equivalentsof cationic nitrogen per kilogram of polymer. One example material isCypro 514.®., a product of Cytec, Inc. of Stamford, Conn. The use ofsuch materials is expressly allowed within the practice of the presentinvention.

The use of high surface area, high anionic charge microparticles for thepurposes of improving formation, drainage, strength, and retention istaught in the art. Common materials for this purpose are silica colloid,or bentonite clay. The incorporation of such materials is expresslyincluded within the scope of the present invention.

If permanent wet strength is desired, the group of chemicals: includingpolyamide-epichlorohydrin, polyacrylamides, styrene-butadiene latices;insolubilized polyvinyl alcohol; urea-formaldehyde; polyethyleneimine;chitosan polymers and mixtures thereof can be added to the papermakingfurnish or to the embryonic web. Polyamide-epichlorohydrin resins arecationic wet strength resins which have been found to be of particularutility. Suitable types of such resins are described in U.S. Pat. Nos.3,700,623 and 3,772,076. One commercial source of usefulpolyamide-epichlorohydrin resins is Hercules, Inc. of Wilmington, Del.,which markets such resin under the mark Kymene 557H.®.).

Many paper products must have limited strength when wet because of theneed to dispose of them through toilets into septic or sewer systems. Ifwet strength is imparted to these products, it is preferred to befugitive wet strength characterized by a decay of part or all of itspotency upon standing in presence of water. If fugitive wet strength isdesired, the binder materials can be chosen from the group consisting ofdialdehyde starch or other resins with aldehyde functionality such asCo-Bond 1000.® offered by National Starch and Chemical Company, Parez750.® offered by Cytec of Stamford, Conn. and the resin described inU.S. Pat. No. 4,981,557 issued on Jan. 1, 1991, to Bjorkquist andincorporated herein by reference.

If enhanced absorbency is needed, surfactants may be used to treat thetissue paper webs of the present invention. The level of surfactant, ifused, is preferably from about 0.01% to about 2.0% by weight, based onthe dry fiber weight of the tissue paper. The surfactants preferablyhave alkyl chains with eight or more carbon atoms. Exemplary anionicsurfactants are linear alkyl sulfonates, and alkylbenzene sulfonates.Exemplary nonionic surfactants are alkylglycosides includingalkylglycoside esters such as Crodesta SL-40.® which is available fromCroda, Inc. (New York, N.Y.); alkylglycoside ethers as described in U.S.Pat. No. 4,011,389, issued to W. K. Langdon, et al. on Mar. 8, 1977; andalkylpolyethoxylated esters such as Pegosperse 200 ML available fromGlyco Chemicals, Inc. (Greenwich, Conn.) and IGEPAL RC-520.® availablefrom Rhone Poulenc Corporation (Cranbury, N.J.).

The present invention is further applicable to the production ofmulti-layered tissue paper webs. Multilayered tissue structures andmethods of forming multilayered tissue structures are described in U.S.Pat. Nos. 3,994,771; 4,300,981; 4,166,001; and European PatentPublication No. 0 613 979 A1. The layers preferably comprise differentfiber types, the fibers typically being relatively long softwood andrelatively short hardwood fibers as used in multi-layered tissue papermaking. Multi-layered tissue paper webs resultant from the presentinvention comprise at least two superposed layers, an inner layer and atleast one outer layer contiguous with the inner layer. Preferably, themulti-layered tissue papers comprise three superposed layers, an inneror center layer, and two outer layers, with the inner layer locatedbetween the two outer layers. The two outer layers preferably comprise aprimary filamentary constituent of relatively short paper making fibershaving an average fiber length between about 0.5 and about 1.5 mm,preferably less than about 1.0 mm. These short paper making fiberstypically comprise hardwood fibers, preferably hardwood Kraft fibers,and most preferably derived from eucalyptus. The inner layer preferablycomprises a primary filamentary constituent of relatively long papermaking fiber having an average fiber length of least about 2.0 mm. Theselong paper making fibers are typically softwood fibers, preferably,northern softwood Kraft fibers. Preferably, the majority of theparticulate filler of the present invention is contained in at least oneof the outer layers of the multi-layered tissue paper web of the presentinvention. More preferably, the majority of the particulate filler ofthe present invention is contained in both of the outer layers.

The tissue paper products made from single-layered or multi-layereduncreped tissue paper webs can be single-ply tissue products ormulti-ply tissue products.

The term “dust” is used herein to refer to the tendency of a tissuepaper web to release fibers or particulate fillers as measured in acontrolled abrasion test, described infra. Dust can be related tostrength since the tendency to release fibers or particles is directlyrelated to the degree to which such fibers or particles are anchoredinto the structure. As the overall level of anchoring is increased, thestrength will be increased. However, it is possible to have a level ofstrength which is regarded as acceptable but have an unacceptable levelof dust. This is because dust can be localized. For example, the surfaceof a tissue paper web can be prone to dust, while the degree of bondingbeneath the surface can be sufficient to raise the overall level ofstrength to quite acceptable levels. In another case, the strength canbe derived from a skeleton of relatively long papermaking fibers, whilefiber fines or the particulate filler can be insufficiently bound withinthe structure. The tissue paper webs of the present invention arerelatively low in lint. Levels of lint below about 12 are preferable,and below about 10 are more preferable.

The multi-layered tissue paper webs of to the present invention can beused in any application where soft, absorbent multi-layered tissue paperwebs are required. Particularly advantageous uses of the multi-layeredtissue paper web of this invention are in toilet tissue and facialtissue products. Both single-ply and multi-ply tissue paper products canbe produced from the webs of the present invention.

Application of a Chemical Softening Agents to Paper Webs

In accordance with the present invention, chemical softening agents maybe applied to a paper web by any application method known in theindustry such as, for example, spraying, printing, extrusion, brushing,by means of permeable or impermeable rolls and/or pads. In a firstembodiment, the claimed softening agent may be applied to a paper webwith a slot die. Specifically, the chemical softening agent may beextruded onto the surface of a paper web via a heated slot die. The slotdie may be any suitable slot die or other means for applying chemicalsoftening agent to the paper web. The slot die or other glue applicationmeans may be supplied by any suitable apparatus. For example, the slotdie may be supplied by a heated hopper or drum and a variable speed gearpump through a heated hose. The chemical softening agent is preferablyextruded onto the surface of the paper web at a temperature that permitsthe chemical softening agent to bond to the paper web. Depending on theparticular embodiment, the chemical softening agent can be at leastpartially transferred to rolls in a metering stack (if used) and then tothe paper web.

Additionally, the chemical softening agent may be applied to a paper webby an apparatus comprising a fluid transfer component. The fluidtransfer component preferably comprises a first surface and a secondsurface. The fluid transfer component further preferably comprises poresconnecting the first surface and the second surface. The pores aredisposed upon the fluid transfer component in a non-random pre-selectedpattern. A fluid supply is operably connected to the fluid transfercomponent such that a fluid (such as the chemical softening agent) maycontact the first surface of the fluid transfer component. The apparatusfurther comprises a fluid motivating component. The fluid motivatingcomponent provides an impetus for the fluid to move from the firstsurface to the second surface via the pores. The apparatus furthercomprises a fluid receiving component comprising a paper web. The paperweb comprises a fluid receiving (or outer) surface. The fluid receivingsurface may contact droplets of fluid formed upon the second surface.Fluid may pass through pores from the first surface to the secondsurface and may transfer to the fluid receiving surface.

The fluid transfer component may comprise a hollow cylindrical shell.The cylindrical shell may be sufficiently structural to function withoutadditional internal bracing. The cylindrical shell may comprise a thinouter shell and structural internal bracing to support the cylindricalshell. The cylindrical shell may comprise a single layer of material ormay comprise a laminate. The laminate may comprise layers of a similarmaterial or may comprise layers dissimilar in material and structure. Inone embodiment the cylindrical shell comprises a stainless steel shellhaving a wall thickness of about 0.125 inches (3 mm). In anotherembodiment (not shown) the fluid transfer component may comprise a flatplate. In another embodiment the fluid transfer component may comprise aregular or irregular polygonal prism.

The fluid application width of the apparatus may be adjusted byproviding a single fluid transfer component of appropriate width.Multiple individual fluid application components may be combined in aseries to achieve the desired width. In a non-limiting example, aplurality of stainless steel cylinders each having a shell thickness ofabout 0.125 inches (3 mm) and a width of about 6 inches (about 15 cm)may be coupled end to end with an appropriate seal—such as an o-ringseal between each pair of cylinders. In this example, the number ofshells combined may be increased until the desired application width isachieved.

The fluid transfer component preferably further comprises poresconnecting the first surface 110 and the second surface. Connecting thesurfaces refers to the pores each providing a pathway for the transportof a fluid from the first surface 110 to the second surface. In oneembodiment, the pores may be formed by the use of electron beam drillingas is known in the art. Electron beam drilling comprises a processwhereby high energy electrons impinge upon a surface resulting in theformation of holes through the material. In another embodiment, thepores may be formed using a laser. In another embodiment, the pores maybe formed by using a drill bit. In yet another embodiment, the pores maybe formed using electrical discharge machining as if known in the art.

In one embodiment, an array of pores may be disposed to provide auniform distribution of fluid droplets to maximize the ratio of fluidsurface area to applied fluid volume. In one embodiment, this may beused to apply a chemical softening agent in a pattern of dots tomaximize the potential for adhesion between two surfaces for any volumeof applied chemical softening agent.

The pattern of pores upon the second surface may comprise an array ofpores having a substantially similar diameter or may comprise a patternof pores having distinctly different pore diameters. In an alternativeembodiment, the array of pores may comprise a first set of pores havinga first diameter and arranged in a first pattern. The array furthercomprises a second set of pores having a second diameter and arranged ina second pattern. The first and second patterns may be arranged tointeract each with the other.

Alternatively, the chemical softening agent may be sprayed directly ontothe surface of a paper web using equipment suitable for such a purposeand as well known to those of skill in the art.

Analytical and Testing Procedures

A. Density

The density of multi-layered tissue paper, as that term is used herein,is the average density calculated as the basis weight of that paperdivided by the caliper, with the appropriate unit conversionsincorporated therein. Caliper of the multi-layered tissue paper, as usedherein, is the thickness of the paper when subjected to a compressiveload of 95 g/in² (15.5 g/cm²).

B. Dispensing Dust Test Method

Dust is measured using a particle counter commercially available(Sympatec QICPIC, Sympatec GmbH, Am Pulverhaus 1, 38678Clausthal-Zellerfeld, Germany). The instrument is used according to themanufacturer's recommendation and a frame rate of 400 frames/sec isselected. The particle size range is set to 20 to 10,000 micrometers.Sympatec's standard chute for guiding particles into the instrument wasmodified by removing the flights within the chute and by attaching afunnel to the top of the chute. The funnel is constructed of stainlesssteel and has 4 trapezoidal sides, 14 inches across the wide part (top),tapering to 2 inches wide at the bottom, i.e. point of attachment withthe chute. The trapezoid sides are 12 inches long. A vacuum is attachedto the exit of the instrument to create an air flow through theinstrument, and consequently the chute and the funnel. The vacuum issufficient to create an airspeed entering the funnel of 470 feet/min.The airspeed is measured using an Extech Instruments ThermoAnemometerModel 407113 and Anemometer metal probe, SN Q138487. The probe wasmounted in a plastic tube in a square of foam (necessitated by thesquare shape of the funnel). The probe assembly was placed in the funnelso that the foam sealed against the funnel walls and the anemometer wascentered above the shaft opening. The linear flow was calculated for thebottom of the funnel where the drop shaft begins (the 2″x2″ opening).

To perform the dust test, sanitary tissue product is dispensed, i.e.pulled apart at the perforations, manually at the top of the funnel torelease dust. The force to rupture the product at the perforations is afunction of the dispensing tensile and the operator merely appliesenough force directly in tension across the perforations to dispense theproduct in a manner typical of tissue dispensing. Care should be takennot to tear the product across any perforations, rather it should bedispensed by pulling directly in tension across the perforations. Thedust fibers and/or particles so liberated are directed into a modifiedSympatec chute and the chute, delivers them to the measurement zone ofthe instrument by gravity and vacuum.

The QICPIC measures the number of particles passing through themeasurement zone using dynamic image analysis. Five perforations areseparated per measurement and the Raw Dispensing Dust value is simplythe total number of particles counted.

The raw data needs to be normalized for width of the product at theperforations. The Raw Dispensing Dust value is multiplied by the widthof the product at the perforations in inches and divided by 4.27. Thisresult is the Dispensing Dust value. Products more than about 6″ wideshould be precut in width with scissors to 4.27 inches wide prior totesting to prevent being too wide to dispense properly in tension. TheNormalized Dispensing Dust value is determined by any one of thefollowing relationships: 1) Dispensing Dust value divided by DispensingTensile and multiplied by 150 yields the Tensile Normalized DispensingDust value; 2) Dispensing Dust Value divided by Lint test result andmultiplied by 7 yields the Lint Normalized Dispensing Dust value; and 3)Dispensing Dust value divided by the product Density and multiplied by0.08 yields the Density Normalized Dispensing Dust value.

The calculated dust valves as related to the application rate to thepaper web (in lb/ton) and application method (spray, extrusion, orprinting) compared to a non-treated paper web area provided in Table 1below.

TABLE 1 Calculated Dust Valves (in # particles) Compared to ApplicationRate of Chemical Softening Agent to Substrate and Application Method andDust Reduction Application Rate of Chemical Softening Spray ExtrusionPrint None Agent to Substrate (particles) (particles) (particles)(particles) 10 lb/ton 6435 5080 6485 7510 Percent Dust Reduction 14.3%32.4% 13.6% — 20 lb/ton 5815 5325 — 7510 Percent Dust Reduction 22.6%29.1% — —

C. Measurement of Panel Softness of Tissue Papers

Ideally, prior to softness testing, the paper samples to be testedshould be conditioned according to Tappi Method #T4020M-88. Here,samples are preconditioned for 24 hours at a relative humidity level of10 to 35% and within a temperature range of 22° to 40° C. After thispreconditioning step, samples should be conditioned for 24 hours at arelative humidity of 48 to 52% and within a temperature range of 22° C.to 24° C.

Ideally, the softness panel testing should take place within theconfines of a constant temperature and humidity room. If this is notfeasible, all samples, including the controls, should experienceidentical environmental exposure conditions.

Softness testing is performed as a paired comparison in a form similarto that described in “Manual on Sensory Testing Methods”, ASTM SpecialTechnical Publication 434, published by the American Society for Testingand Materials 1968 and is incorporated herein by reference. Softness isevaluated by subjective testing using what is referred to as a PairedDifference Test. The method employs a standard external to the testmaterial itself. For tactile perceived softness two samples arepresented such that the subject cannot see the samples, and the subjectis required to choose one of them on the basis of tactile softness. Theresult of the test is reported in what is referred to as Panel ScoreUnit (PSU). With respect to softness testing to obtain the softness datareported herein in PSU, a number of softness panel tests are performed.In each test ten practiced softness judges are asked to rate therelative softness of three sets of paired samples. The pairs of samplesare judged one pair at a time by each judge: one sample of each pairbeing designated X and the other Y. Briefly, each X sample is gradedagainst its paired Y sample as follows:

1. a grade of plus one is given if X is judged to may be a little softerthan Y, and a grade of minus one is given if Y is judged to may be alittle softer than X;

2. a grade of plus two is given if X is judged to surely be a littlesofter than Y, and a grade of minus two is given if Y is judged tosurely be a little softer than X;

3. a grade of plus three is given to X if it is judged to be a lotsofter than Y, and a grade of minus three is given if Y is judged to bea lot softer than X; and, lastly:

4. a grade of plus four is given to X if it is judged to be a whole lotsofter than Y, and a grade of minus 4 is given if Y is judged to be awhole lot softer than X.

The grades are averaged and the resultant value is in units of PSU. Theresulting data are considered the results of one panel test. If morethan one sample pair is evaluated then all sample pairs are rank orderedaccording to their grades by paired statistical analysis. Then, the rankis shifted up or down in value as required to give a zero PSU value towhich ever sample is chosen to be the zero-base standard. The othersamples then have plus or minus values as determined by their relativegrades with respect to the zero base standard. The number of panel testsperformed and averaged is such that about 0.2 PSU represents asignificant difference in subjectively perceived softness.

Calculations

All results are in units of grams/inch. For purposes of thisspecification, the tensile strength should be converted into a “specifictotal tensile strength” defined as the sum of the tensile strengthmeasured in the machine and cross machine directions, divided by thebasis weight, and corrected in units to a value in meters.

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact dimension and values recited.Instead, unless otherwise specified, each such dimension and/or value isintended to mean both the recited dimension and/or value and afunctionally equivalent range surrounding that dimension nand/or value.For example, a dimension disclosed as “40 mm” is intended to mean “about40 mm”.

All documents cited in the Detailed Description of the Invention are, inrelevant part, incorporated herein by reference; the citation of anydocument is not to be construed as an admission that it is prior artwith respect to the present invention. To the extent that any meaning ordefinition of a term in this document conflicts with any meaning ordefinition of the same term in a document incorporated by reference, themeaning or definition assigned to that term in this document shallgovern.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

1. A tissue paper product having at least one ply, wherein only one outer surface of said tissue paper product has a chemical softening agent applied and substantially affixed thereto, said chemical softening agent providing said tissue paper product with a raw dispensing dust value, said raw dispensing dust value being at least about 13.6 percent less than a raw dispensing dust value of a tissue paper product not having said chemical softening agent applied and substantially affixed thereto.
 2. The tissue paper product of claim 1, wherein said raw dispensing dust value is at least about 14.3 percent less than said raw dispensing dust value of said tissue paper product not having said chemical softening agent applied and substantially affixed thereto.
 3. The tissue paper product of claim 2, wherein said chemical softening agent is sprayed onto said one outer surface of said tissue paper product.
 4. The tissue paper product of claim 2, wherein said raw dispensing dust value is at least about 22.6 percent less than said raw dispensing dust value of said tissue paper product not having said chemical softening agent applied and substantially affixed thereto.
 5. The tissue paper product of claim 4, wherein said chemical softening agent is applied to said one outer surface of said tissue paper product at a rate of about 20 lbs. per ton.
 6. The tissue paper product of claim 1, wherein said raw dispensing dust value is at least about 29.1 percent less than said raw dispensing dust value of said tissue paper product not having said chemical softening agent applied thereto.
 7. The tissue paper product of claim 6, wherein said chemical softening agent is extruded upon said one outer surface of said tissue paper product.
 8. The tissue paper product of claim 7, wherein said raw dispensing dust value is at least about 32.4% less than said raw dispensing dust value of said tissue paper product not having said chemical softening agent applied and substantially affixed thereto.
 9. The tissue paper product of claim 8, wherein said chemical softening agent is applied to said outer surface of said tissue paper product at a rate of about 10 lbs. per ton.
 10. The tissue paper product of claim 9, wherein said chemical softening agent is printed upon said one outer surface of said tissue paper product.
 11. The tissue paper product of claim 1, wherein said chemical softening agent is selected from the group consisting of quaternary ammonium compounds, polysiloxanes, and combinations thereof.
 12. The tissue paper product of claim 11, wherein said quaternary ammonium compound has the formula: (R₁)_(4-m)—N⁺—[(CH₂)_(n)—Y—R₂]_(m)X⁻ wherein: m is 1 to 3; each R₁ is a C₁-C₆ alkyl or alkenyl group, hydroxyalkyl group, hydrocarbyl or substituted hydrocarbyl group, alkoxylated group, benzyl group, or mixtures thereof; each R₂ is a C₁₄-C₂₂ alkyl or alkenyl group, hydroxyalkyl group, hydrocarbyl or substituted hydrocarbyl group, alkoxylated group, benzyl group, or mixtures thereof; and, X⁻ is any softener-compatible anion.
 13. The tissue paper product of claim 11, wherein said quaternary ammonium compound has the formula: (R₁)_(4-m)—N⁺—[(CH₂)_(n)—Y—R₃]_(m)X⁻ wherein: Y is —O—(O)C—, or —C(O)—O—, or —NH—C(O)—, or —C(O)—NH—; m is 1 to 3; n is 0 to 4; each R₁ is a C₁-C₆ alkyl or alkynyl group, hydroxyalkyl group, hydrocarbyl or substituted hydrocarbyl group, alkoxylated group, benzyl group, or mixtures thereof; each R₃ is a C₁₃-C₂₁ alkyl or alkynyl group, hydroxyalkyl group, hydrocarbyl or substituted hydrocarbyl group, alkoxylated group, benzyl group, or mixtures thereof; and X⁻ is any softener-compatible anion.
 14. A through-air dried tissue paper product having at least one ply, wherein only one outer surface of said tissue paper product has a chemical softening agent applied and substantially affixed thereto, said chemical softening agent providing said tissue paper product with a raw dispensing dust value of less than about
 6485. 15. The through-air dried tissue paper product of claim 14, wherein said chemical softening agent is printed onto said one outer surface.
 16. The through-air dried tissue paper product of claim 14, wherein said raw dispensing dust value is less than about
 5815. 17. The through-air dried tissue paper product of claim 16, wherein said chemical softening agent is sprayed onto said one outer surface.
 18. The through-air dried tissue paper product of claim 14, wherein said raw dispensing dust value is less than about
 5325. 19. The through-air dried tissue paper product of claim 18, wherein said raw dispensing dust value is less than about
 5080. 20. The through-air dried tissue paper product of claim 18, wherein said chemical softening agent is extruded onto said one outer surface. 